useradd-staticids.bbclass: improve error message

useradd-staticids.bbclass: improve error message

Current error message is difficult to read:

ERROR: Nothing PROVIDES 'image'
trs-image was skipped: image - image: normal username test does not have a static ID defined. Add test to one of these files

It's not clear that first "image" is recipe name, second "image" is
binary package name and that "test" is the user account which does not
have a static ID defined. Improve the error message so that these are
more explicit. Now the error message looks like:

image was skipped: Recipe image, package image: normal username "test" does not have a static ID defined.

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>